Design justification

Initially, three alternative designs were suggested based on the location detection mechanism, tracking mechanism, and hardware used. These three designs were (1) marker-based AR game; (2) hybrid AR/VR game; and (3) markerless AR game.

1. Marker-based AR. In the first design, a mobile game in which ghosts are lo- cated in some physical items around the campus was suggested. The player must find these items and exorcise the ghosts that "live" in them before the time limit. Why the idea was dropped?

(a) Asking the user to scan items will make the game more predictable mean- ing it loses the element of surprise.

(b) Using marker-based AR requires orchestration (setting up the QR codes or markers in the campus) which will decrease the scalability of the game. (c) Using hand gestures can interfere with the marker-based tracking system

since the user’s hand might hide the marker while interacting with the sys- tem.

2. Hybrid AR + VR. The second idea involved both AR and VR technologies. The players would be asked to find hidden “portals” (QR codes/markers) that can take them to the ghost’s world (a virtual world) where they can fight them. Why the idea was dropped?

(a) The same with the “Marker-based AR”, using marker-based AR will make the game poorly scalable.

(b) Using VR in smart glasses (ODG R7 ) with hand gestures as input is not practical since the glasses are OST, which makes the VR experience not engaging.

3. Markerless AR. The third design involved making a markerless AR game which means an AR solution that does not use any markers or target images, an example of this would be Pokemon GO. Since the game is a role playing game where the player takes the role of a ghost hunter who uses “futuristic goggles” to see and capture the ghosts that live in the campus, the markerless AR is perfect for the story.

5.3. Game concept

Ghost Hunters, is an AR “catch the monsters” game where the player takes the role of a ghost hunter equipped with high-tech goggles that allows him/her to see ghosts and capture them. The goggles are used to see ghosts and capture them using a “virtual laser” generated by the glasses. The goggles (in-game) use the light of the environment to charge, this means that the players must constantly find bright areas to keep their goggles on. To beat the game, the player must capture all the ghosts that move in the campus area, which can only be reached by moving (walking) to them in real life. The

game has two losing conditions, the player runs out of time (3 minutes) or the Goggles’ battery reaches 0%.

Figure 18. The hand gestures used in Ghost Hunters.

The gesture that the player has to perform in order to capture a particular ghost depends on the ghost type that he/she is seeing. To make the interactions more natural, the “paper, rock, and scissors” gestures were used to interact with the ghosts which have the same three types including rock, paper, and scissors. In order to capture these ghosts, the player has to do the gestures that can beat that type of ghosts as if he/she is playing a real paper, rock, scissors game against it (Figure 18). This means that a rock ghost can be captured with a paper hand gesture, paper ghost can be captured with a scissors hand gesture, and the scissors ghost can be captured with rock hand gesture. The reason behind using the paper, rock, scissors as metaphor is that this traditional game is popular with a well known hand gestures that are easy to explain and describe to test users.

5.4. Interaction methods

For the interaction methods, hand gestures and buttons were used. The hand gesture interface is the same for both devices (smart phone and smart glasses). However, for the button interface, the smart phone version have virtual buttons while the smart glasses have physical buttons and that is because the smart glasses’ displays are not touch sensitive.

5.4.1. Hand gestures

The first interaction method is the natural hand gestures. As explained before, the game uses the traditional paper, rock, scissors as a metaphor to make the game interaction easy for the users. Using hand gestures is the natural way of playing the traditional game, so using them in a digitized version of the game should facilitate the learning process and make it easier for the players to interact with the ghosts. Figure 18 illus- trates the three different hand gestures that the game recognize. Each of these gestures should be displayed clearly in the front camera as shown in the figure exactly in order

for the application to recognize them. This was mentioned explicitly to the second and third field trial round participants before they tried the application since the first trial round revealed that the participants did not know how to interact with the application without explaining them in detail how to perform the hand gestures. For instance some users were using the hand gestures properly, but their hands were out of the camera FoV, so it was impossible for the application to detect the hand gestures.

5.4.2. Buttons

The alternative way of interaction is using buttons. Having both the buttons and the hand gestures interaction methods in the same application will provide insights about interaction techniques in both smartphone and smart glasses. Each button was associ- ated with a unique gesture. For smartphones, the buttons were virtually displayed on the screen and the players can tab them in order to use them. However, for the smart glasses, physical buttons were implemented since the users cannot interact with the virtual buttons without a physical device provided by the ODG called the speed mouse (Figure 19).

Figure 19. The ODG’s Speed Mouse and the buttons used for Ghost Hunters.

The user simply clicks the button that corresponds to the gesture he/she wants to perform like "paper" for instance. So in order to play the game perfectly, the users must memorize the buttons functionalities which is assumed to be a difficult task in such short amount of time.